Melt the butter and marshmallows by heating 3 tablespoons of butter in a saucepan over medium heat. Add 10 ounces of mini marshmallows, stirring continuously until melted and smooth, about 3-5 minutes.

Remove from heat and stir in green food coloring until fully incorporated.

Fold in 6 cups of Rice Krispies until evenly coated with the gooey mixture.

Press the mixture into a greased 9x13-inch baking dish, aiming for a thickness of about 1 inch.

Cool the bars at room temperature for about 30 minutes until firm.

Cut into squares or rectangles.

Decorate with chocolate chips, candy eyes, and black icing.

Serve immediately or store in an airtight container.